The present invention relates to a method for determining the rotor position of a stationary or slowly rotating synchronous machine by evaluating electrical test pulses that are obtained by applying voltage pulses to the individual phase windings of the stator, wherein changes in the inductance of the phase windings which are caused by saturation of the stator iron depending on the rotor position, are determined in opposite directions of current by calculating differences in the amount of current of two test pulses, and angle values being predetermined by the number of the phase windings are associated with the differences in the amount of current.
A method of this type is e.g. disclosed in U.S. Pat. No. 6,172,498 B1 being titled ‘Method and Apparatus for Rotor Angle Detection’. When the prior art method is implemented, test pulses of opposite polarity are applied to the individual phase windings of the stator, and difference values are produced from the pulses' amplitudes which are used to determine the general rotor position and, subsequently, to determine a correction value used to correct the general rotor position.
It is disadvantageous in this method that the residual magnetism of the stator iron being induced by the test pulses influences in each case the following test pulse so that the initial rotor position is not determined with a sufficient rate of accuracy, with the result that the measuring accuracy of the method is highly impaired.